Treatment of cracked distillates



W. E. KUHN June 7, 1938.

TREATMENT 0F CRCKED DISTILLATES Filed Jan. 8, 1937 WAYNE E KUHN INVENTOR T'roRNEYJ Patented June 7, 1938 l TREATMENT 0F CRACKED DISTILLATES Wayne E. Kuhn, Port Arthur, Tex., assignor to The Texas Company, New York,

poration of Delaware N. Y., a cor- Application January s, lssmlsenal No. 119,540

(o1. 19e-iol Claims.

This invention relates to the treatment of 'cracked distillates to produce an increased yield of high quality finished gasoline.

v'I'he invention contemplates broadly the sep- 5 aration of a crackedv distillate into lighter and heavier fractions, subjecting the heavier fraction to a refining operation to remove impurities, separating from the lighter fraction normally gaseo'us hydrocarbons undesired in the finished gasoline, combining theremainder of the lighter fraction with the refined heavier fraction, subjecting said normallyffgaseous hydrocarbons to polymerization to 'form add tional gasoline hy;A

drocarbons, separating the lpl'lymer naphtha fror'n polymer naphtha to the system to undergo treatment in conjunction with said cracked distillate.

More particularly, in accordance with the invention, a naphtha distillate requiring strong refining treatment is subjected, preferably after the separation of .xed gases, to fractionation to separate the naphtha into a lighter portion requiring no drastic 'renin'g treatment and a heavier portion which is subjected to rather drastic refining to remove impurities, such as sulfur compounds and unstable color and gum forming hydrocarbons. The lighter `portion is thereafter fractionated to remove therefrom the more volatile constituents unsuitable for inclusion in the finished gasoline. The remainder of the light portion is then combined with the treated heavier portion to produce a nished gasoline.

,The more volatile materials removed from the light fraction, comprising normally gaseous hydrocarbons, are subjected to polymerization to form normally liquid hydrocarbons suitable for gasoline manufacture. These normally' liquid hydrocarbons are separated from the polymerization products and returned to the system for treatment in conjunction with the cracked distillate to increase the yield and improve the quality of the finished product.

The following description of the invention should be read in vconnection with the accompanying drawing which shows in elevation a sketch of apparatus suitable for carrying out the process of the invention.

Referring to the drawing, a charging stock which, may be a cracked distillate from an adjacent cracking still or other refinery motor fuel distillate, comprising normally gaseous hydrocarbons suitable for polymerization and gasoline constituents requiring refining treatment, as herein described, is passed through the line i controlled by valve 2 to accumulator 3. This the polymerization products and returning said.

accumulator may be connected with cracking ,y stills and maintained under considerable pressure, for example around 200 pounds, and at a temperature of about 100-125 F. The product collected in the accumulator 3 ordinarily contains all or a portion of the gaseous hydrocar.- bons evolved in previous cracking or formation of the distillate. A portion of the gaseous materials, preferably the fixed or unco'ndensable I gases, such as hydrocarbons of one and two car- 1o bon atoms and a portionof the hydrocarbons of three carbon atoms, are released from the top' of accumulator 3 through valve controlled line 5. The distillate is then drawn from the bottom of the accumulator through the'line 6 controlled y15 by valve l and forced by the pump 8 through the line l0 to a fractionator l2. .In this fractionator or debutanizer, a fraction comprising hydrocarbons of four carbon atoms and lighter is separated and passed through the vapor line I3 controlled by valve M to a secondary fractionator l5. Considerably lower pressure, 'for' example around to 100 pounds, may be maintained on the fractionator I2 than on the accumulator 3. It is intended that a lighter cut requiring no drastic chemical treatment be separated from a heavier cut requiring such; drastic treatment. About 20 to 40%, preferably around 30% of such light fraction is ordinarily removed in the fractionator l2.

The heavier cut is removed from the bottom of the fractionator 'I2 through the line I8, controlled by valve I9. This fraction ordinarily contains impurities such as sulfur compounds and unsaturated color and gum forming hydrocarbons which are undesirable in thefinished gasoline and require rather drastic treatment with refining agents to effect their removal'. The treatment applied to the fraction may include one or more operations such as treatment with '40 adsorptive materials, such as fullers earth in the vapor or liquid phase, acid treatment, alkali washes, etc. The heavy naphtha is forced by .the pump 20 through the line 2| to mixing chamber 22 wherein it is intimately mixed with a remixer 22 may be any suitable type of apparatus for effecting contact between the acid and the oil, such as a stirring mechanism, orifice plates, or a suitable type of apparatus for carrying out an operation involving the counter-current flow principle. Products from the mixer 22 overflow through the line 30 to settler 3| wherein the acid sludge settles out and may be withdrawn from the bottom of the settler through the valve controlled line 32. It is to be understood that one or more settlers, washing and neutralizing chambers may be employed. The acid treated product which may be previously washed, neutralized and rerun is withdrawn from the top of the settler 3| through line 34 controlled by valve 35, and combined with a lighter portion of the gasoline in the line 36. The mixture so formed may be suitable for use as a motor fuel or be further treated, for example by sweetening.

The lighter portion of the distillate, separated in the fractionator I2 and conducted to the fractionator I5, -is subjected to fractionation in the fractionator or depropanizer I to separate the lighter normally gaseous hydrocarbons undesired in the finished gasoline. In this fractionator the hydrocarbons of three carbon atoms and all or a portion of those of four carbon atoms are separated. The remainder of the lighter cut is withdrawn from the bottom of the fractionator I5 through the line 36, controlled by valve 3l, and combined with the refined heavier cut, as referred to heretofore. The normally gaseous hydrocarbon fraction, including a portion or all of butane and propane, is withdrawn from the top of the fractionator I5 through the line 40 controlled by valve 4I.

It is intended that this gaseous hydrocarbon fraction be subje Y normally hydrocarbons suitable for manufacture of gasoline. A thermal or=.cata1ytic hi l y unsaturated it may be advantageous to usi a catalytic polymerization operation in which the oleiins are polymerized in the presence of a catalyst such as phosphoric acid. If the gases are largely saturated, it is'Y preferable to use a thermal polymerization operation. In the drawing an apparatus intended".for carrying out a thermal polymerization is shown. For this purpose, the gases in the'line 4II are forced by the pump 42 to a heating coil 44 located in a heater 45. Conditions maintained in the coil 44 are -those commonly used in thermal polymerization, for example vpressures of 50G-5000 pounds and temperatures of 900-1;100 F., preferably pressures of about 2000 pounds and temperatmes of around 1050 F. The reaction products are transferred through the line 46 in which may be located a heat exchanger, not shown, to fractionator 48. In the fractionator 48 the normally liquid hydrocarbons are separated as a polymer naphtha which may be withdrawn from the bottom thereof through the line 49 controlled by valve 50.

The polymer naphtha so withdrawn is forced by .pump 52 located in the line 49 through the line 53 back to the system to undergo treatment in conjunction with the cracked distillate. This naphtha is preferably combined with the distillate to be treated prior to separation into the lighter and heavier fractions and may be so combined, either in accumulator drinn 3 or the' fractionator I2. In the drawing means are shown for combining the two in the fractionator I2. It will be understood that polymer naphtha may be introduced into the accumulator 3 and the latter may be advantageous in case appreciable amounts of xed gases are present in this naphtha.

All or a portion of the Cs and C4 hydrocarbons may be retained in the polymer. However, it is preferable, particularly in a thermal polymerization operation such as carried'out in the apparatus in the drawing, that the C3 hydrocarbons and all or a portion of the C4. hydrocarbons be separated in the fractionator 48 and withdrawn from the top thereof through the line 55 and introduced into the secondary fractionator 56. In the latter fractionator, materials lighter than the C; hydrocarbons are separated and released from the top of the fractionator through the valve controlled line 51. 'I'he heavier gaseous fractions comprising C3 and C4 hydrocarbons are withdrawn from the bottom of the fractionator through the lin'e 58, controlled by valve 60 and recycled by the pump 6I through the line 62 back to the heating coil 44.

As an example of the operation of the invention, cracked distillate, such as that found in the accumulator drum of a cracking still used for cracking heavy oils under heat and pressure in the liquid and Vapor phase, and in which the fixed gases, such as methane, ethane, ethylene and a portion of the propylene and propane have been released, is subjected to fractionation or debutanization. In the debutanization operation approximately 30% of the light constituents including C3 and C4 hydrocarbons are separated from the naphtha bottoms. The heavier fraction or naphtha bottoms is subjected to acid treatment with sulfuric acid and after separation of the sludge, washed, neutralized and preferably redistilled. The lighter fraction from the debutanizer is subjected to further fractionation or depropanization to separate materials lighter than C4 hydrocarbons 'and as much of the C4 hydrocarbons as required to give the proper Volatility of. the nished gasoline. 'I'he remainder of the lighter fraction or bottoms from the depropanizer is then combined with the acid treated heavier `cut and the mixture further treated, for example by lsweetening if necessary, to form a finished gasoline. The overhead from thedepropanizer, comprising normally gaseous hydrocarbons chiefly of three and four carbon atoms, is `then subjected to thermal polymerization under a pressure of about 2000 pounds and temperature of about 1050 F. and time of about 90 seconds, whereby a substantial amount of normally liquid hydrocarbons is formed. A polymer naphtha corresponding to over"50% conversion is separated from the polymeriz ion products and returned to the system for "retreatment Since the polymer naphtha may require refining treatments similar to those given to the cracked distillate, this polymer naphtha is combined with the cracked distillate in the debutanizer and thereafter is subjected to the refining treatment heretofore described as given to the cracked distillate. The nished gasoline, comprises the original cracked distillate and polymer naphtha. 'I'his finished product is a high quality motor fuel having an antiknock value of 75 or higher.

The present invention provides a unitary process for treating cracked distillates to obtain a maximum yield of high quality finished gasoline. The process has the advantage of utilizing the rejected lighter materials from the cracked distillate by converting them into an additional quantity of gasoline. The polymer naphtha obtained from these ordinarily rejected gaseous hydrocarbons is furthermore advantageously recombined with the cracked distillate prior to the refining treatment of the cracked distillate whereby both products are rened in one operation. `In vthisjway. the Ygasoline constituents of both the crackeddistillate and the polymer K naphtha are ref llidnd recovered as a finished polymerization. According to the process vof the* gasoline while the' lighter normally gaseous components are accumulated and subjected to thermal invention, increas `yields are obtained and the blending and treating`of .the products are accom-- plished inV a more economical and facile manner. By blending the cracked distillate and polymer naphtha prior to treating, the eiliciency and -quality of the operation are increased because of lthe modifyingv effects, obtained by the presence of .the two ingredientsinr the mixture.

Obviously many modi'cations and variations of. the invention, as hereinbefore set forth, may

be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. v l

`I claim:

1. A process for the treatment of cracked distillates, which comprises separating the distillate into lighter and heavier fractions, subjecting the heavier fraction to a refining operation to remove Iimpurities, separating normally gaseous hydrohydrocarbons to polymerization, separating a.

polymer naphtha from the polymerization products and commingling said polymer naphtha with the cracked naphtha to be treated.

3. A process for the treatment of cracked distillates, which comprises separating the distillate into lighter and heavier fractions, acid treating the heavierfraction, separating from the vlighter fraction less volatile portion suitable for gasoline,

combining the said less volatile portion with the acid treated heavier portion, subjecting a more volatile portion of the light fraction to polymerization, recovering a polymer naphtha from the polymerization products, and combining `the polymer ,naphtha with the cracked distillate prior to separation thereof into lighter and heavier fractions.

4. A process for the treatment of cracked motor fuel distillates, 4which comprises separating from -the distillate lxedY gases consistingmainly of hydrocarbons of one and two carbon atoms, 1

then fractionating to separate a lighter portion amounting to around 30% acid treating the remaining heavier portion,. separating from. the

lighter portion 'normally gaseoushydrocarbons comprising C3 and'C4A hydrocarbons and readding the remainder of the lighter portion to the treat- ,ed heavier portion, subjecting said normally gaseous hydrocarbons to polymerization, recovering a polymer naphtha from the polymerization productsand returning said naphtha to the system to be treatedl in conjunction with said cracked distillate. v

5. A* process for the treatment of cracked distiliates, which' comprises separating the distill te into lighter and heavier fractions, subjecting` t e heavier fraction to relining to remove impurities. fractionating the lighter fraction into a norma-ily gaseous hydrocarbon fraction and higherv boiling fraction comprising light ends of gasoline, retain;

ing a substantial amount ofC4 hydrocarbons in said fraction comprising light ends of gasoline. blending said fraction comprising light ends of gasoline with the refined heavier fraction to obtain a productof about gasoline voiatilitynsuir-vl jecting said normally gaseous hydrocarbon fraction to polymerization, separating a polymer naphtha, and returning said polymer naphtha to the rst mentioned separation operation.

WAYNE E. 

